This R01 application is one of four coordinated R01 Grants whose primary focus is the prospective characterization of effects on variation in the early social, emotional and behavioral problems of young children of gene-environment interplay (GE correlation and GxE interaction). This R01 makes use of a children-of-twins (COT) paradigm, building upon a prospective study of female like-sex twin pairs who were first assessed in adolescence (N=3277 twins assessed at wave 4 in early adulthood, ages 18-26). The COT design is particularly powerful for resolving (i) GE correlation effects associated with partner selection, (ii) GE correlation effects arising because heritable traits in parents predict increased probability of offspring high risk environmental exposures. Hypothesis-testing will be integrated within a theoretical framework that considers 3 meta-models -(behavioral under-control/disinhibition; behavioral inhibition/negative affect; pharmacologic impairment/substance dependence) for understanding how genetic and phenotypic differences between young women, in combination with differences in early experience (childhood trauma, rearing environment), contribute to risk of a progressive cascade of environmental risk for their present or future offspring. Gene-environment interplay is considered from a developmental perspective that considers pre-conception effects (partner selection, relationship formation), prenatal effects (early versus delayed pregnancy, maternal smoking and drinking during pregnancy), immediate post-natal environment (family socioeconomic disadvantage, high-risk neighborhood), early family environment (parent-parent relationship and relationship dissolution, and parenting behaviors; early traumatic events) and external environmental influences (access to high quality day-care, schooling). Two waves of data collection from the young adult female twin pairs, by telephone interview (target N=2622 interviews at wave one, N=2490 interviews at 2-year follow-up) will characterize relationship and pregnancy histories and early parenting behavior, perceived partner behavioral and emotional problems (projected N=2100 partners, with 20 percent completing interviews at each wave) and children's emotional and behavioral problems (projected N=2000 offspring), and will obtain updated assessments of twin risk-factors. In conjunction with R01s 2-4, these data will permit a powerful resolution of hypotheses concerning GE interplay effects on young children.